A power conversion device based on switching of a power semiconductor element is widely used for consumers, vehicles, railroads, and transformer facilities, because the power conversion device has high conversion efficiency. Because the power semiconductor element generates heat by energization, a high heat radiation property is required. Generally, a metal heat radiation structure having fins is used in the heat radiation and the heat radiation structure is connected to a ground (GND) to stabilize a potential and prevent electric shock. For this reason, an insulating material disposed between the power semiconductor element and the heat radiation structure needs to have superior thermal conductivity. However, when a voltage to be converted is high, it is necessary to increase a thickness of the insulating material to improve an insulation property, so that a heat radiation property is deteriorated.
As an example of a method of improving the heat radiation property, a method of sandwiching a conductor to be a material with high thermal conductivity between insulating layers, which is disclosed in PTL 1, is known.